Safety paper and method of making the same



Patented Mar. 16, 1937 UNITED STATES SAFETY PAPER AND METHOD OF MAKING THE SAME Burgess W. Smith, Rochester, N. Y., assignor to I, e Todd Company, Inc., Rochester, N. Y., a corporation of New York No Dr win pplication August 22,1932, Serial 4 Claims. (01. 91-67.95)

This invention relates to safety papers for making bank checks, drafts, bonds, or other documents in which it is desired that erasures made with chemical ink eradicators be indicated by a 5 stain or discoloration and method of making the same.

The object of my invention is to provide a more practical and efficient paper of this character, capable of being inexpensively manufactured in the desired commercial form and a more practical and efficient method of making the same. More particularly, it is the object of the invention to provide a paper which will be quickly and conspicuously discolored by the action of ink eradicator, regardless of the order of application of its components, or its acidity, as well as'the method of making the same.

To these and other ends, the invention resides in certain improvements, combination of parts, and method steps, all of which will be more fully described, the novel features being pointed out, in the claims at the end of this specification.

In the preparation of the class of safety papers in which the use of ink eradicators produces a stain, the active ingredient for maximum efficiency should possess certain characteristics. The material should be relatively stable to normal influences, and the stain when produced should resist removal by reagents commonly known and used for this purpose. It should react with the commonly used ink eradicator, which is composed of an alkaline hypochlorite, generally hypochlorite of soda, used in combination with a second component consisting of a solution of tartaric acid. For maximum efficiency it should react in either acid or alkaline condition of the hypochlorite of soda or other eradicator.

I have found that compounds having two benzene rings, linked togetherby the linkage \O=X --NH/ in which the component X may be S, O, NH,

with at least one amino radical on each ring pa a to that linkage, will develop a conspicuous stain with hypochlorite of soda ink eradicators i in any order of application or in either alkaline or acid condition.

Compounds of this class are represented by p,p'-diaminodiphenylthiourea, p, p diaminodi phenyl'guanidine, p,p'-diaminotriphenylguanidine, or any other compound having a substitution for the X component that retains the aforesaid characteristic of color development with acid hypochlorite such as exhibited, for example, by p,p-diaminodiphenylthiourea.

I prefer the use of p,p'-diaminodiphenylthiourea inasmuch as it may be easily and cheaply prepared in a high order of purity by the interaction of carbon disulfide and p-phenylenediamine, two chemicals made commercially in large quantities, and readily accessible at a low price.

In the form of the base this compound is reasonably stable, but it is much more so in the form of its salts, of which the sulfate is probably the most stable. The sulfate, having a high degree of insolubility, may be incorporated in the paper in that form when the paper is being made, by the introduction in the beater, the Jordan, or by sprinkling or otherwise applyingit to the web in process of formation.

It may be precipitated as the sulfate from the hydrochloride, which may be in a state of solution in the beater, or in any other suitable stage in the process of manufacturing paper, such as the incorporation of it in the sizing.

I may use such a compound in an ink prepared with any of the commercially known varnish mediums,-or use a more novel medium which is a solution of cellulose nitrate in diethylene phthalate. Inks of this nature may be applied as a general surface coating, or used to form a warning word or symbol such as is described in my Patent No. 1,454,837.

The quantities and proportions used for this purpose depend entirely on the desired depth of stain or discoloration, and the application of this material involves no special skill not possessed by one familiar with this art.

Paper having incorporated therein or thereon organiccompounds of the class described will inhomologues and analogues of the compounds named, and other methods of application of these compounds, as are well understood by those skilled in this art, may be used without departing from the spirit of this invention.

It is to be further understood that the term paper containing means that the material may be on the surface alone, incorporated in a film intimately attached thereto, or in the body of the paper. The term safety paper means any paper or writing surface on which it is desired to indicate the application of a chemical ink eradicator by the production of a stain or discoloration.

I claim:

1. A safety paper containing a salt of p,p'-diaminodiphenylthiourea adapted to react to produce a visible discoloration upon the application of a chemical ink eradicator.

2. A method of making safety paper comprising the step of adding the sulfate of p,p'-diamlnodiphenylthiourea during or after the formation of the web for the purpose of producing, by its reactions, a visible indication of the use of a chemical ink eradicator.

3. A safety paper containing a sulfate of p,p'- diaminodiphenylthiourea, adapted to react to produce a visible discoloration upon the application of a chemical ink eradicator.

4. The method of making safety paper comprising the addition to the paper of a salt of p,p'-diaminodiphenylthiourea, adapted to react to produce a visible discoloration upon the application of a chemical ink eradicator.

BURGESS W. SMITH. 

